1. Field of the Invention
The present invention relates to apparatus and method for characterizing subsurface materials from within a borehole penetrating the subsurface materials.
2. Description of the Related Art
Boreholes are drilled deep into the earth for many applications such as hydrocarbon production, geothermal production, and carbon dioxide sequestration. It is important to obtain accurate measurements of properties of subsurface materials of interest in order to efficiently use costly drilling and production resources. Typically, the measurements are performed with a downhole tool configured to be disposed in a borehole penetrating the subsurface materials in order to get close to the subsurface materials of interest.
One category of measurements is detecting and measuring radiation. The radiation can be electromagnetic such as gamma rays or particles such as neutrons. Also, the radiation can be natural or it can be induced by radiation emitted from the downhole tool. To measure radiation, the downhole tool includes a radiation detector sensitive to a particular type of radiation of interest. To be able to measure radiation accurately and reliably, the radiation detector must be able to operate and survive in a downhole environment. Unfortunately, very high temperature environment can exist deep in the borehole. In addition, when the downhole tool is disposed in a bottomhole assembly near a drill bit on a drill string, the radiation detector can be exposed to high levels of vibration and shock from drilling. It would be well received in the drilling industry if radiation detectors could be built to withstand the high temperatures and accelerations that exist in a downhole environment.